As a Sound engineer for many a decade, If I get a 50/50 split of opinion between people at the front complaining that "It's too loud" and people at the back complaining "It's too quiet" I've probably got it about right.
Unless one brings another van with extra amps/speakers/additional cabling/delay lines etc. It's not an easy option to satisfy everyone. And believe me there are some people who will never be satisfied!